[Common] Avoid zero-initialising the NN TPC PID prediction buffer

The per-DataFrame prediction buffer (masked tracks x output dims x 9 mass
hypotheses, ~72 MB for a 1M-track PbPb DataFrame) is a value-initialised
std::vector: a full memset touching every page, immediately overwritten in
full by the per-hypothesis evaluation loop. Carry it as an uninitialised
unique_ptr<float[]> instead, so each page is touched once, by the write that
fills it. All consumers only read it under useNetworkCorrection, so the null
buffer with the network disabled is never dereferenced. No change to any
computed value.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DgKXVM9Q9Hcgexfyj7Eqpp

Author: ktf

Common/Tools/PID/pidTPCModule.h

@@ -443,11 +443,8 @@ class pidTPCModule
 
   //__________________________________________________
   template <typename TCCDB, typename M, typename T, typename B>
-  std::vector<float> createNetworkPrediction(TCCDB& ccdb, soa::Join<aod::Collisions, aod::EvSels> const& collisions, M const& mults, T const& tracks, B const& bcs, const size_t size)
+  std::unique_ptr<float[]> createNetworkPrediction(TCCDB& ccdb, soa::Join<aod::Collisions, aod::EvSels> const& collisions, M const& mults, T const& tracks, B const& bcs, const size_t size)
   {
-
-    std::vector<float> network_prediction;
-
     auto start_network_total = std::chrono::high_resolution_clock::now();
     if (pidTPCopts.autofetchNetworks) {
       const auto& bc = bcs.begin();
@@ -505,7 +502,10 @@ class pidTPCModule
     const uint64_t track_prop_size = input_dimensions * size;
     const uint64_t prediction_size = output_dimensions * size;
 
-    network_prediction = std::vector<float>(prediction_size * 9); // For each mass hypotheses
+    // Deliberately uninitialised: the evaluation loop below writes every element
+    // (one block per mass hypothesis), so zero-initialising would only touch
+    // every page of an O(100 MB) buffer twice.
+    std::unique_ptr<float[]> network_prediction(new float[prediction_size * 9]); // For each mass hypotheses
     const float nNclNormalization = response->GetNClNormalization();
     float duration_network = 0;
 
@@ -624,7 +624,7 @@ class pidTPCModule
 
   //__________________________________________________
   template <typename T, typename NSF, typename NST>
-  void makePidTables(const int flagFull, NSF& tableFull, const int flagTiny, NST& tableTiny, const o2::track::PID::ID pid, const float tpcSignal, const T& trk, const int64_t multTPC, const std::vector<float>& network_prediction, const int& count_tracks, const int& tracksForNet_size)
+  void makePidTables(const int flagFull, NSF& tableFull, const int flagTiny, NST& tableTiny, const o2::track::PID::ID pid, const float tpcSignal, const T& trk, const int64_t multTPC, const float* network_prediction, const int& count_tracks, const int& tracksForNet_size)
   {
     if (flagFull != 1 && flagTiny != 1) {
       return;
@@ -750,7 +750,7 @@ class pidTPCModule
     reserveTable(pidTPCopts.pidTinyAl, products.tablePIDTinyAl);
 
     const uint64_t tracksForNet_size = (pidTPCopts.skipTPCOnly) ? totalTPCnotStandalone : totalTPCtracks;
-    std::vector<float> network_prediction;
+    std::unique_ptr<float[]> network_prediction;
 
     if (pidTPCopts.useNetworkCorrection) {
       network_prediction = createNetworkPrediction(ccdb, cols, pidmults, tracks, bcs, tracksForNet_size);
@@ -951,7 +951,7 @@ class pidTPCModule
       }
 
       auto makePidTablesDefault = [&trk, &tpcSignalToEvaluatePID, &multTPC, &network_prediction, &count_tracks, &tracksForNet_size, this](const int flagFull, auto& tableFull, const int flagTiny, auto& tableTiny, const o2::track::PID::ID pid) {
-        this->makePidTables(flagFull, tableFull, flagTiny, tableTiny, pid, tpcSignalToEvaluatePID, trk, multTPC, network_prediction, count_tracks, tracksForNet_size);
+        this->makePidTables(flagFull, tableFull, flagTiny, tableTiny, pid, tpcSignalToEvaluatePID, trk, multTPC, network_prediction.get(), count_tracks, tracksForNet_size);
       };
 
       makePidTablesDefault(pidTPCopts.pidFullEl, products.tablePIDFullEl, pidTPCopts.pidTinyEl, products.tablePIDTinyEl, o2::track::PID::Electron);